The flickering pile of tails and gaping mouths is placed on a scale and weighs in at 90 kg, which distributer Phy Veasna says should fetch about $187.

Men unload fish into a metal tank at Chbar Ampov market in Phnom Penh’s Meanchey district last week. (Siv Channa/The Cambodia Daily)

Since he started his business in 2012, Mr. Veasna has been importing Trey Phtok from Vietnam, along with the rest of the nearly one ton of fish he sells each day.

“In Cambodia we don’t have fish,” he said earlier this week. “If Cambodian fish were available I wouldn’t need to buy and sell Vietnamese fish.”

But Cambodia does have fish, lots of them.

Cambodia’s inland freshwater fisheries—among the richest in the world thanks to large floodplains around the Tonle Sap lake and the country’s major rivers—are the most intensively exploited on earth, according to the WorldFish Center, a Malaysia-based research non-profit.

Cambodia ranks fourth in the world behind China, India and Bangladesh in the productivity of its fresh water capture fisheries, according to the organization.

“We have an abundance of wild fish [in Cambodia]. It’s amazing how many wild fish there is here in terms of volume,” said Alan Brooks, WorldFish’s Greater Mekong Region director.

According to inland fishery statistics, he estimated that about 500,000 tons of fish are naturally produced per year.

However, much of the wild fish caught here is smuggled out of the country, meaning the robust trade in freshwater fish is not reflected in official government trade figures, said Youk Senglong, program manager at the Fisheries Action Coalition Team (FACT).

In the first quarter of this year, the value of fishery exports increased 26 percent from $203,309 in 2013 to $256,173 this year. The total value of fishery exports last year was $934,824—a fraction of the almost $7 billion in exported goods.

Most of Cambodia’s fish stocks are being caught in Cambodian waters and transported to markets in Vietnam, said Mr. Senglong.

“Illegal fishing is increasing, especially at night time and in places far from the eyes of communities and civil society,” he said. “They use both legal and illegal fishing gear.”

Mr. Senglong said well-equipped and well-funded groups of fishermen, often from Vietnam, will pay bribes of about $500 to authorities to turn a blind eye, pushing out small-scale local fishing operations.

Locals are sometimes left to take matters into their own hands.

In May, 13 Vietnamese nationals raiding the waters off the coast of Kampot province were apprehended by Cambodian fishermen who banded together on 70 small fishing boats to surround two 22-meter boats.

On a good night, a 5 to 10 member fishing crew can bring in a haul worth in excess of $5,000, which is then ferried back to Vietnam, according to Mr. Senglong.

A number of officials at the Ministry of Agriculture’s Fisheries Administration declined to comment, while an assistant of Nao Thuok, director of the administration, declined requests for an interview.

As Cambodia’s fish are being taken out of the country, the demand for fish in the country is being met mostly by factory fish farms in Vietnam.

For sellers like Mr. Veasna, fish caught in Cambodian waters are simply too expensive to sell on the domestic market. He buys Trey Phtok from Vietnamese fish farms for $1.80 per kg and sells it for about $2.10. For the same fish naturally sourced in Cambodia, he would have to pay $2.60 per kg.

“Natural fish in Cambodia are more expensive than Vietnamese fish,” he said. “So I import from Vietnam.”

The influx of cheap farm-raised fish from across the border is also suppressing the expansion of Cambodian fish farms.

At a fish farm in Russei Keo district, dead fish shimmer on the surface of a disused pond. Srey Mao, the owner of the farm, said she has had to scale down operations due to falling demand.

From 2008 to 2012, Ms. Mao was earning about $17.50 per day from selling her baby fish to other farmers to raise to maturity. But since mid-2012, she says sales have dropped to $2.50 per day at best.

To afford the $3,000 rent per year for her 2,150 square meter farm, Ms. Mao has had to lay off the seven workers she used to employ.

“Our business has been going down because my customers have stopped farming,” she said.

Tanarith Nay, a 42-year-old surgeon who retreats to his two-hectare fish farm on the outskirts of Phnom Penh when he’s not working, said the costs of running a farm have been on the rise.

The 400 tons of grain he buys every year to feed the fish on his farm costs $0.25 per kg this year, up from $0.21 per kg in 2013. Mr. Nay said Vietnamese fish farmers use artificial methods to quickly fatten their fish for export, leaving Cambodian farmers struggling to keep up.

“The quality of Vietnamese fish is not good because they pump their fish with artificial food so they’re ready to sell in two months, whereas mine take about two years to fully grow,” he said.

Mr. Brooks at WorldFish said total aquaculture production is actually growing by about 10 to 15 percent per year, or about 90,000 tons annually. But Cambodia’s fish farmers are at a significant disadvantage in their competition with farmers across the border.

“If you have large amounts of fish that are being imported or dumped in Cambodia then it’s going to suppress a fairly nascent industry,” said Mr. Brooks.

“It’s tempting to say we should beat them at their own game and be more efficient. But [Vietnam has] high-tech intensive systems and the country is so close,” he added. “And I wouldn’t recommend any border tariffs because it will be tit-for-tat after that.”

And the fisheries sector is a vital source of income and food for more than 6 million people and represents more than 10 percent of gross domestic product, according to a 2010 report from WorldFish.

“Cambodians are among the highest consumers of freshwater fish in the world, with annual per capita fish consumption estimated at 52.4 kg,” says the report, titled Aquaculture For the Poor in Cambodia–Lessons Learned.

“Food security in Cambodia has traditionally had two dimensions: rice and fish, with fish being a central aspect of rural livelihood strategies. More than 80 percent of the total animal protein in the Cambodian diet is estimated to come from fish and aquatic animals, especially from inland water bodies, namely paddy fields, rivers, streams, natural lakes and community ponds,” the report says.

However, Yang Saing Koma, president of the Cambodian Center for Study and Development in Agriculture, said that creating a sustainable domestic fish supply depends on a strong aquaculture industry. But starting and running a fish farm is not easy, or cheap. The initial outlay is about $1,000, at the least, and it can take up to five years for an investment to be returned, he said.

“There is a quickly growing urban population so there’s a big demand for fish…natural fishing is seasonal and cannot supply fish all year round so we need to develop aquaculture,” he said. “However it is not profitable as you need a lot of skill, capital and access to water all year round.”

For Ms. Mao, the time for aquaculture industry to gain traction is running out.

“If business is bad like this for another year we will have no choice but to close down and move to planting something such as vegetables.”